Lane identification method and related apparatus thereof

ABSTRACT

A lane identification method for identifying a lane whereon a vehicle is traveling, which includes: providing a drive video; generating an identification result of recognizing a plurality of lane lines corresponding to the line according the drive video, wherein the identification result is generated based on inside borderlines of the lane lines; and determining the lane according to the identification result.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/951,483 filed on Jul. 26, 2013. The contents of theseapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosed embodiments of the present invention relate to videoprocessing, and more particularly, to lane identification methodapparatus in a lane departure warning system for detecting if a vehicledeparts from its lane by lane.

2. Description of the Prior Art

The lane departure warning system is an active driving safety techniquefor detecting if a vehicle departs from its lane. When a driver drives avehicle to depart from the current lane without utilizing a blinker dueto mental incompetence or negligence, the lane departure warning systemwill detect this abnormal situation and issue a warning message toremind the driver to drive the vehicle back to the lane.

The existing lane departure warning system architecture can be dividedinto the following types: the image sensing type, the laser sensingtype, and the infrared sensing type. The most common type is the imagesensing type, and this type of lane departure warning system will recordthe drive video first, analyze the drive video, and judge if lanedeparture occurs according to the current lane identified by referringto images of the road.

However, the roadway is usually marked by various kinds of lane lineswith different shapes (e.g., solid lines, dotted lines, broken lines,solid double lines, broken double lines, solid/broken lines, andchannelizing lines), and also there are various kinds of signs andsymbols painted on the roadway, thus making the lane identificationprocess complicated. For example, the lane departure warning system hasto compare the lane markings in the drive video with all of the knownlane lines by using complex algorithms, which usually requires a largeamount of computation to complete. In addition, the accuracy of the laneidentification is also influenced by environmental factors. For example,the poor and bad weather, including the night time, the rainy weather,etc., causes poor visibility and then makes the lane departure warningsystem hardly to capture clear drive images, which affects the accuracyof lane recognition. Furthermore, unnecessary warnings may be issuederroneously to confuse the driver. Therefore, to improve the accuracy oflane identification and the reliability of a lane departure warningsystem has become an important issue in the field.

SUMMARY OF THE INVENTION

Thus, one of the objectives of the present invention is to provide alane departure warning system and related method, which can adjust thesensitivity adaptively to prevent a driver from the error warningmessages by detecting if the vehicle is traveling in a poor environment.Besides, another one of the objectives of the present invention is toprovide a lane identification method and related apparatus, which canrecognize the lane by detecting the inside borderline of the marking onthe roadway to simplify the lane identification process and furtherimprove the accuracy of lane identification.

According to one embodiment of the present invention, a laneidentification method for identifying a lane whereon a vehicle istraveling is provided. The method comprises: providing a drive video;generating an identification result of recognizing a plurality of lanelines corresponding to the line according the drive video, wherein theidentification result is generated based on inside borderlines of thelane lines; and determining the lane according to the identificationresult.

According to one embodiment of the present invention, a laneidentification apparatus for identifying a lane whereon a vehicle istraveling is provided. The device comprises: an identification module,for generating an identification result of recognizing a plurality oflane lines corresponding to the line according a drive video, whereinthe identification result is generated based on inside borderlines ofthe lane lines; and a determination module, coupled to theidentification module, for determining the lane according to theidentification result.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram illustrating a lane departurewarning system according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating how a determination module selects adetermination strategy in the lane departure warning system of thepresent invention.

FIG. 3 shows a drive video.

FIG. 4 is a flowchart illustrating an embodiment of the lane departurewarning system of the present invention.

FIG. 5 shows a processed drive video.

FIG. 6 is a flowchart illustrating how to generate the identificationresult of the lane line identification.

FIG. 7 is a diagram illustrating how to identify the lane linesaccording to the geometry relationship.

FIG. 8 is a functional block diagram illustrating a lane lineidentification apparatus according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Certain terms are used throughout the description and following claimsto refer to particular components. As one skilled in the art willappreciate, manufacturers may refer to a component by different names.This document does not intend to distinguish between components thatdiffer in name but not function. In the following description and in theclaims, the terms “include” and “comprise” are used in an open-endedfashion, and thus should be interpreted to mean “include, but notlimited to . . . ”. Also, the term “couple” is intended to mean eitheran indirect or direct electrical connection. Accordingly, if one deviceis electrically connected to another device, that connection may bethrough a direct electrical connection, or through an indirectelectrical connection via other devices and connections.

The following description would describe the design principles anddetails of the lane departure warning system and method of the presentinvention. Please refer to FIG. 1, which is a functional block diagramillustrating a lane departure warning system according to an embodimentof the present invention. As shown in FIG. 1, the lane departure warningsystem 100 includes an image sensing device 110, an identificationmodule 120, and a determination module 130. The image sensing device 110is arranged for generating images S_Video. The identification module 120is coupled to the image sensing device 110, and arranged for recognizinga plurality of lane lines corresponding to at least one lane to generatean identification result S_IDTF, wherein the identification resultS_IDTF is generated based on specific borderlines of the lane lines. Thedetermination module 130 is coupled to the identification module 120,and arranged to decide a determination strategy based on vehicle speedinformation SPD_INFO, and generate a determination result S_DEP based onthe determination strategy and the identification result S_IDTF. Thelane departure warning system 100 decides whether to issue a warningS_WARN according to the determination result S_DEP. By way of example,the specific borderline may be an inside borderline of a lane whereon avehicle is traveling.

The details of the determination module 130 would be described first asfollows, and the basic principles and operation instructions of theidentification module 120 would be described later. Please refer to aflowchart shown in FIG. 2. In step 210, the determining module 130 firstselects the determination strategy based on the vehicle speedinformation SPD_INFO. If the vehicle speed information SPD_INFOindicates that the speed of the vehicle being driven by the driver iswithin a first speed range, the determination module 130 would select anaggressive determination strategy (step 240). Under this situation thatthe aggressive determination strategy is selected, when theidentification module 120 indicates that the identified lanes arebecoming less gradually, the aggressive determination strategy wouldmake the determination module 130 generate the determination resultS_DEP which indicates the vehicle has departed from lane (step 250). Forexample, when the identification module 120 has only identified out aright lane line 330 of a lane 310 shown in the drive image of FIG. 3,the determination module 130 can also refer to this information as wellas the lane departure algorithm to generate the determination resultS_DEP which indicates the vehicle has departed from a lane. If adefensive determination strategy is selected (step 220), then thedetermine module 130 would not generate the determination result S_DEPto indicate the vehicle has departed from a lane until there are morelane lines identified by the identification module 120. For example,when the identification module 120 has identified out both the rightlane line 330 and the left lane line 320 of the lane 310 shown in FIG.3, the determination module 130 would generate the determination resultS_DEP which indicates the vehicle has departed from a lane according tothe identification result S_IDTF and the lane departure algorithm.

The foregoing aims at separating different confidence levels in lanerecognition and lane departure determination. In general, when thevehicle speed is high, it often means the vehicle is traveling in asimple environment such as freeway or highway, and also theidentification accuracy would be higher. On the contrary, when thevehicle is traveling in a relative complex environment such as urbanstreets or lanes at the intersection, the roadway is marked by morelines and signs. Too many line markings would probably make theidentification module 120 generate an incorrect identification result inthe lane line identification stage. For example, the non-lane line maybe mistakenly identified as the lane line, thus making the lanedeparture algorithm go wrong. Accordingly, in accordance with thepresent invention, when the vehicle is traveling at high speed, thesensitivity of the lane departure warning system 100 would be increased,while when the vehicle is traveling at low speed, the sensitivity of thelane departure warning system 100 would be decreased. When the vehiclespeed is within the first speed range I (e.g., the speed is 60 km ormore) which is a higher speed range, the aggressive determinationstrategy would be used to calculate the lane departure. In addition,this determination strategy may affect settings of the parameters of thelane departure algorithm. For example, some more lenient conditions fordetermining whether lane departure occurs may be established, andwarnings would be issued if there is any slightest possibility that thevehicle departs from its lane. And in this determination strategy, evenif only one lane line is identified, the lane departure determinationwill also be performed. However, when the vehicle speed is within asecond speed range II (e.g., the speed is lower than 60 km) which is alower speed range, the defensive determination strategy would be used tocalculate the lane departure. It would establish some more stringentconditions for determining whether the lane departure occurs, and issuewarnings only if there is a very affirmative result. And in thisdetermination strategy, more than one lane line is needed to beidentified for allowing the lane departure determination to beperformed.

Furthermore, in addition to determining the strategy according to thevehicle speed information, the strategy may also be determined bydriver-defined information in other embodiments of the presentinvention. In this case, the lane departure warning system of thepresent invention may provide a driver interface for allowing the driverto select one of the defensive determination strategy and the aggressivedetermination strategy. When the driver feels lethargic or can'tconcentrate on driving the vehicle, the lane departure warning systemcan be switched to the aggressive determination strategy from thedefensive determination strategy. In this way, although the error ratemay become higher, but it does in return for better detection rate,thereby reducing any possible risk for achieving better traffic safety.

Moreover, the lane departure warning system of the present invention maybe disposed in any vehicle, and the vehicle speed information may beprovide through a vehicle body signal or a satellite navigation systemwhich is installed on the vehicle.

Through the aforementioned methods, the lane departure warning system100 of the present invention can determine whether to issue a warningS_WARN according to the determination result S_DEP of the determinationmodule 130. However, if the lane departure warning system 100 of thepresent invention receives a braking signal or a blinker signal from thevehicle body signal, the lane departure warning system 100 will notissue any warning even if the determination result S_DEP indicates thevehicle has departed from the lane. This is because the driver probablyhas noticed that the vehicle has departed from the lane, or the driveris currently driving the vehicle to have lane changing.

In an embodiment, the identification module 120 may be a lane lineidentification module equipped with at least the function of the laneline identification, and the determination module 130 may be a lanedeparture determining module equipped with at least a function fordetermining whether the vehicle departs from the lane. Furthermore, theidentification module 120 and the determination module 130 may beimplemented through a variety of manners, such as a processor thatperforms the corresponding software, a pure hardware circuit, or acombination of both. The processor may be a general-purpose processor ora specific processor such as a digital signal processor. The softwaremay be stored in a computer readable medium (e.g., an optical disc, ahard disk, a flash memory, a random-access memory (RAM), a read-onlymemory (ROM), or any other storage device which may be identified andaccessed by the processor, and the software may include all kinds ofprogrammable logics, instructions, or necessary information for theimplementation of the present invention. In addition, in the purehardware circuit architecture, the identification module 120 anddetermining module 130 may include a hard-wired logic, a programmablelogic (e.g., Field Programmable Gate Array, FPGA), or a ComplexProgrammable Logic Device (CPLD), and/or an application-specificintegrated circuit (ASIC). Besides, in other different embodiments ofthe present invention, the identification module 120 and thedetermination module 130 may be realized using the same circuit elementor different circuit elements.

Another embodiment of the present invention provides a laneidentification method which is used for identifying a lane whereon avehicle is traveling. Please refer to the flowchart shown in FIG. 4. Instep 410, a drive video is provided, and the drive video may be providedby an image sensing device. Next, in step 420, the line of the lane towhich a plurality of lane lines correspond may be recognized accordingto the drive video, thereby generating an identification result, whereinthe identification result is generated based on the inside borderline ofthe lane line. Taking FIG. 3 for example, in order to identify thecorrect position of the lane 310 whereon the vehicle is currentlytraveling, at least one of the left lane line 320 and the right laneline 330 of the lane 310 must be identified from the drive video, andthe identification of the lane line can be determined according to theinside borderline of the lane line. Thereafter, in step 430, the lane310 can be determined according to the identification result.

In one embodiment, the step 420 further includes: generating a processeddrive video which includes a plurality of objects. The followingdescription will explain how to produce the processed drive videoincluding a plurality of objects. Please refer to FIG. 5 in conjunctionwith FIG. 3. FIG. 3 represents an original drive video, and FIG. 5 isthe processed drive video. First, when the original drive video shown inFIG. 3 is received, a pre-processing operation will be performed uponthe original drive video. The pre-processing operation is arranged forfiltering the drive video according to the brightness and the geometryof the objects in the drive video. Since the main material of themarkings on the roadway is paint, the markings and lane lines would havesimilar brightness at different lanes or environments and fall within aspecific brightness range regardless of sunlight exposure (day ornight). Furthermore, lane lines are usually solid straight lines orbroken straight lines, and the lane line would therefore present aspecific geometry in the drive video. Based on these principles, thepre-processing operation can filter out the components in the drivevideo which do not meet the requirements of the specific brightness aswell as the specific geometry. For instance, in the original drive videoshown in FIG. 3, the color and the paint material of cars 380 and 390are different from the paint material of the lane lines. Hence, each ofcars 380 and 390 does not meet the requirements of the specificbrightness, and its geometry is far different from that of the lanelines. The cars 380 and 390 will be filtered out during thepre-processing operation. Furthermore, although the color and the paintmaterial of arrow markings 350 and 360 are identical to that of the lanelines, and the arrow markings 350 and 360 therefore show the similarbrightness; however, the geometry of the arrow markings 350 and 360 isdifferent from that of the lane lines, so eventually the arrow markings350 and 360 will be filtered out in the pre-processing operation.Finally, a processed drive video, including objects 322, 324, 326, 332,334, 336, 342, 344, 372, and 374, will be obtained in the pre-processingstage.

After the processed drive video shown in FIG. 5 is obtained, the nextstep is to identify whether objects 322, 324, 326, 332, 334, 336, 342,344, 372, and 374 in FIG. 5 are lane lines or a portion of the lanelines. The flowchart shown in FIG. 6 explains how to generate theidentification result according to the processed drive video. First, instep 610, a video central axis of the processed drive video isdetermined as the central axis C shown in FIG. 5. Next, in step 620,candidate lane line segments are selected from the objects 322, 324,326, 332, 334, 336, 342, 344, 372, and 374, wherein the candidate laneline segments may possibly represent objects of the lane line or aportion of the lane line. Finally, in step 630, the identificationresult would be generated according to the candidate lane line segmentsselected in step 620.

In one embodiment, the step of selecting the candidate lane linesegments from the objects in the processed drive video further includes:when there is no other object between an inside borderline of a specificobject of the objects and the video central axis, determining that thespecific object is one of the candidate lane line segments. First ofall, the definitions of the video central axis and the inside borderlineare explained here. The video central C represents the central positionof the traveling vehicle, and the inside borderline is a borderline ofan object's contour that is relatively close to the vehicle. Therefore,the inside borderline needs to be determined based on the video centralaxis. If an object is located at the left side of the video center axisC, then the right borderline would be regarded as the inside borderline;and if the object is located on the right side of the video center axisC, then the left borderline would be regarded as the inside borderline.After the inside borderline of each object is determined, if an objectis located on the right side of the video center axis C and there is noany other object between the left borderline of the object and the videocentral axis C, then the object is determined to be one candidate laneline segment. Similarly, if an object is located on the left side of thevideo center axis C and there is no any other object between the rightborderline of the object and the video central axis C, then the objectis determined to be one candidate lane line segment. This process canhelp to exclude the lane lines which do not belong to the lane 310whereon the vehicle is traveling. For instance, in the processed drivevideo shown in FIG. 5, due to the fact that there are objects 332, 334,and 336 between the left borderline of the object 342 and 344 (which arepart of the right double yellow solid line 340) and the video centralaxis C, the objects 342 and 344 would not be treated as the lane linecandidate segments. Similarly, due to the fact that there are objects322, 324, and 326 between the right borderline of the objects 372 and374 within the lane line 370 of the left lane 311 and the video centralaxis C, the objects 372 and 374 would not be treated as the lane linecandidate segments. Therefore, only objects 322, 324, 326, 332, 334, and336 will be selected as the candidate lane line segments.

After the candidate lane line segments are decided, it is required todetermine whether the candidate lane line segments are able toconstitute a lane line. This is determined by checking if there is anyspecific geometric relationship between the candidate lane linesegments. In the processed drive video shown in FIG. 5, the candidatelane line segments 322, 324, 326, 332, 334, and 336 are not arranged ina straight line. However, there must have a geometric relationshipbetween the candidate lane line segments for constituting a completelane line. For example, the candidate lane line segments 322, 324 and,326, which constitute the lane line 320, are substantially parallel to areference straight line L′, and the candidate lane line segments 332,334 and, 336, which constitute the lane line 330, are substantiallyparallel to a reference straight line L. Furthermore, the candidate laneline segments 322, 324 and 326 are adjacent and arranged with moderateintervals. The candidate lane line segments meeting these conditionswill be regarded as a lane line. The example shown in FIG. 7 illustratesthe condition that the candidate lane line segments will not be regardedas a lane line. As shown in FIG. 7, due to the fact that the objects720-760 are located on the right side of the video central axis C andthere is no other object in between the video central axis C and objects720-760, the objects 720-760 are regarded as the candidate lane linesegments. However, the objects 720, 730, and 740 are parallel to thereference straight line L, but the objects 750 and 760 are not. Hence,the objects 750 and 760 do not belong to the lane line to which theobjects 720, 730, and 740 belong. Furthermore, since the spacing betweenobject 740 and objects 720, 730 is too large (i.e., not adjacent to eachother), so the object 740 does not belong to the lane line to which theobjects 720 and 730 belong. The final result therefore shows that onlythe objects 720 and 730 belong to the same lane line.

The identification result obtained through the aforementioned steps willdecide the left and right lane lines of the current driving lane. Forexample, in the example of FIG. 3, the left and right lane lines 320 and330 of the current driving lane 310 are decided. Hence, the specificlocation of the current driving lane 310 can be confirmed, therebyachieving the purpose of lane identification. The above-mentionedprocess and method can be integrated into the above-described lanedeparture warning system and method. That is to say, the identificationmodule 120 may use the above process to recognize lane lines by firstfinding out the candidate lane line segments according to the drivevideo and accordingly identifying the lane lines corresponding to thecurrent driving lane to generate the identification result, and thengenerating the determination result according to different strategies,where the determination result indicates whether lane departure occurs.Please note that not all of the lane lines 320 and 330 are required tobe identified for performing lane departure determination, as a matterof fact that it depends on the determination strategy employed by thelane departure warning system and method.

Based on the above-mentioned lane identification method, a laneidentification apparatus is provided in another embodiment of thepresent invention. Please refer to the functional block diagram shown inFIG. 8, which illustrates a lane identification apparatus according toan embodiment of the present invention. As shown in FIG. 8, the laneidentification apparatus 800 includes an identification module 810 and adetermination module 820. The identification module 810 is utilized torefer to a drive video S_video (possibly the lane video before or afterpre-processed) for identifying a plurality of lane lines correspondingto a lane and accordingly produce an identification result S_IDFT,wherein the identification result S_IDFT is generated based on theinside borderlines of the lane lines. The identification module 820would select a video central axis of the drive video according to theaforementioned process, and then select the lane line segments from thedrive video in accordance with the video central axis. Finally, lanelines of the current driving lane would be determined to generate theidentification result S_IDFT. The determination module 820 is coupled tothe identification module 810, and arranged to determine the specificlocation of the current driving lane based on the identification resultS_IDFT.

The above-mentioned lane departure warning method and landidentification method may be implemented through pure softwarearchitecture, a pure hardware circuit, or through a combination of theboth. For instance, the lane departure warning method and landidentification method may be implemented through a processor thatperforms the corresponding software, through a pure hardware circuit, orthrough a combination of both. The processor may be a general-purposeprocessor or a specific processor such as a digital signal processor.The software may be stored in a computer readable medium (e.g., anoptical disc, a hard disk, a flash memory, a random access memory (RAM),a read-only memory (ROM), or any other storage device which may beidentified by the processor, and the software includes all kinds ofprogrammable logics, instructions, or necessary information for theimplementation of the present invention. In addition, a specific circuitrealized by a hard-wired logic, a programmable logic (e.g., FieldProgrammable Gate Array, FPGA), a Complex Programmable Logic Device(CPLD), or an application-specific integrated circuit (ASIC) may beincluded in the pure hardware circuit architecture.

In summary, the present invention simplifies the process of the laneline identification and improves the accuracy of it by detecting theinside borderline of markings on the roadway and then determiningwhether the markings are lane lines or a portion of lane lines.Furthermore, in the lane departure warning system of the presentinvention, one of the determination strategies could be selectedaccording to the vehicle speed information for providing differentlevels of sensitivity, thereby making the lane departure warning systemof the present invention more reliable.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A lane departure warning method for a vehicle,comprising: providing a drive video; generating an identification resultof recognizing a plurality of lane lines according the drive video,wherein the identification result is generated based on insideborderlines of the lane lines, comprising: generating a processed drivevideo which includes a plurality of objects; determining a video centralaxis of the processed drive video; selecting a plurality of candidatelane line segments from the objects according to the video central axis,comprising: when there is no other object between an inside borderlineof a specific object of the objects and the video central axis,determining the specific object is one of the candidate lane linesegments; and generating the identification result according to theplurality of candidate lane line segments; determining a lane whereonthe vehicle is traveling according to the identification result;determining a sensitivity of lane departure warning according to a speedat which the vehicle is traveling; and determining whether to issue awarning according to the determined lane and the sensitivity.
 2. Thelane departure warning method of claim 1, wherein the step of generatingthe processed drive video comprises: performing a pre-processingoperation upon the drive video, which selects the objects from the drivevideo that meet a specific brightness requirement and a specificgeometry requirement.
 3. The lane departure warning method of claim 1,wherein the step of determining that the specific object is one of thecandidate lane line segments comprises: when the specific object islocated at a left side of the video center axis, determining thespecific object is one of candidate the lane line segments if there isno other object between a right borderline of the specific object andthe video central axis; and when the specific object is located at aright side of the video center axis, determining the specific object isone of the candidate lane line segments if there is no other objectbetween a left borderline of the specific object and the video centralaxis.
 4. The lane departure warning method of claim 1, wherein the stepof generating the identification result according to the candidate laneline segments comprises: checking if there is any specific geometricrelationship between the candidate lane line segments; and treating thecandidate lane line segments as a lane line when there is specificgeometric relationship between the candidate lane line segments.
 5. Thelane departure warning method of claim 4, wherein the specific geometricrelationship comprises angle relationship with respect to the videocentral axis and neighboring relationship with respect to othercandidate lane line segments.
 6. A lane departure warning apparatus fora vehicle, comprising: an identification module, for generating anidentification result of recognizing a plurality of lane lines accordinga drive video, wherein the identification result is generated based oninside borderlines of the lane lines; a video processing module, forgenerating a processed drive video which includes a plurality ofobjects; a determination module, coupled to the identification module,for determining a lane whereon the vehicle is traveling according to theidentification result; determining a video central axis of the processeddrive video; selecting a plurality of candidate lane line segments fromthe objects according to the video central axis by determining aspecific object is one of the candidate lane line segments when there isno other object between an inside borderline of a specific object of theobjects and the video central axis; generating the identification resultaccording to the plurality of candidate lane line segments; determininga sensitivity of lane departure warning according to a speed at whichthe vehicle is traveling; and determining whether to issue a warningaccording to the determined lane and the sensitivity.
 7. The lanedeparture warning apparatus of claim 6, wherein the video processingmodule performs a pre-processing operation upon the drive video, whichselects the objects from the drive video that meet a specific brightnessrequirement and a specific geometry requirement.
 8. The lane departurewarning apparatus of claim 6, wherein: when the specific object islocated at a left side of the video center axis, the identificationmodule determines the specific object is one of candidate the lane linesegments if there is no other object between a right borderline of thespecific object and the video central axis; and when the specific objectis located at a right side of the video center axis, the identificationmodule determines the specific object is one of the candidate lane linesegments if there is no other object between a left borderline of thespecific object and the video central axis.
 9. The lane departurewarning apparatus of claim 6, wherein the identification module checksif there is any specific geometric relationship between the candidatelane line segments; treats the candidate lane line segments as a laneline when there is specific geometric relationship between the candidatelane line segments.
 10. The lane departure warning apparatus of claim 9,wherein the specific geometric relationship comprises angle relationshipwith respect to the video central axis and neighboring relationship withrespect to other candidate lane line segments.